Fluorescent brightening compositions



Patented Oct. 28, 1969 3,475,172 FLUORESCENT BRIGHTENING COMPOSITIONS Alan Bright, Miroslav V. Mijovic, and David G. Saunders, Wealdstone, Harrow, England, assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed June 28, 1966, Ser. No. 561,012 Claims priority, application Great Britain, July 1, 1965,

Int. Cl. G03c 1/92; C09k 1/02 US. or. 96-82 16 Claims ABSTRACT OF THE DISCLOSURE Fluorescent compositionscomprising an intimate mixture of (l) at least one Water-soluble fluorescent agent .which-has strong absorption of radiation in the ultraviolet This invention relates to fluorescent compositions for incorporation in compositions of matter and more particularly to fluorescent agent-solvent compositions and to photographic light-sensitive"elements containing these -fluores'c'ent compositions.

It is known to-inco'rporatefluorescent compounds in various compositions of matter such as fluorescent paints, inks, plasticizers, etc.

The whiteness in monochrome and color photographic prints may be enhanced by various methods which have been proposed from time to time. For instance, the prints may be bathed in a solution of a fluorescent whitening agent before drying, but such treatment may be suflicient to enhance the whiteness in the low density areas of the print and tends to cause a bloom in the high density areas of the prints. It has been proposed to incorporate a fluorescent whitening agent beneath the light-sensitive layers of monochrome or color light-sensitive material. In copending Knott et al., US; application Ser. No. 275,370, filed Apr. 24, 196-3, now abandoned, in favor of continuation-in-part application, U.S. Ser. No. 373,020, now'U.S. Patent 3,434,837, issued Mar. 25, 1969, photographic color materials are described and claimed in which a fluorescent brightening agent is incorporated as a solution or dispersion in an organic solvent.

' We have found that the stability of the fluorescent compounds dispersed in a high-boiling point solvent and incorporatedin 'black-and-white and color print materials is" dependent On the choice of solvent. 7

One object of our invention is to provide a novel fluorescent composition which produces an increased amount of fluorescence upon exposure to activating light and which has substantially improved fluorescent stability upon prolonged exposure to activating light. Another object of our invention is to provide a novel com position containing (1) a fluorescent agent' which has strong absorption of radiation in'th'e ultraviolet region of the spectrum, high fluorescent emission in the blue region of the spectrum and which is substantially insoluble in water, and (2) a solvent dispersing agent for the fluorescent agent, which composition is strongly fluorescent, has substantially improved fluorescent stability to prolonged exposure to light and which is advantageously incorporated in various compositions of matter, such as photographic elements, fluorescent paints, inks, plasticizers, etc. Another object of our invention is to provide photographic light-sensitive elements which have at least one novel layer containing a hydrophilic colloid having dispersed therein an intimate mixture of (1) a fluorescent agent which has strong absorption of radiation in the ultraviolet region of the spectrum, high fluorescent emission in the blue region of the spectrum and whichis substantially insoluble in Water, and (2) a solvent dispersing agent for the fluorescent agent. Still other objects will become apparent from a consideration of the following specification and claims.

These and other objects of our invention are accomplished with novel fluorescent compositions which in their simplest form comprise an intimate mixture of:

(1) A fluorescent agent which has strong absorption of radiation in the ultraviolet region of the spectrum, high fluorescent emission in the blue region of the spectrum and which is substantially insoluble in water, and

(2) A diester derived from a dibasic monocyclic aromatic acid and an alkyl-substituted cyclohexanol as a dispersing solvent for the fluorescent agent.

Our fluorescent compositions also advantageously contain combinations of fluorescing agents and/ or combinations of diesters'derived from dibasic monocyclic aromatic acids and alkyl-substituted cyclohexanols. Our fluorescent compositions provide strong fluorescence and have substantially improved fluorescent stability to prolonged exposure to light as compared to fluorescent compositions known before.

Our fluorescent compositions are used to advantage for incorporation in various compositions and matter where fluorescence is desired such as in fluorescent paints, inks, plasticizers, and in particular, in light-sensitive photographic materials where itis desired to increase the whiteness of the highlight areas in either black-and-white prints or in color prints. Y

The diesters derived from a dibasic monocyclic aromatic acid and an alkyl-substituted cyclohexanol used to advantage according to our invention include those represented by the following formula:

wherein R and R each represent an alkyl group, preferably having from 1 to 4 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, etc.; R ,..R R and R each represent a member such as a hydrogen atom, and an alkyl group, preferably having from 1 to 4 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, etc.

Typical examples of diesters of Formula I include the following:

Any fluorescent agent which absorbs radiation in the ultraviolet region of the spectrum, having high fluorescent emission in the blue region of the spectrum and .which is substantially insoluble in water is advantageously used according to our invention. Useful fluorescent agents includes stilbene, coumarin and thiophene fluorescent agents. Among such fluorescent agents are the following:

(II) Zr in which Y and Y, are alkyl groups, Z and Z, are hydrogen or alkyl groups, n is the integer 1 or 2, R R R R and R are aryl, alkyl, alkoxy, aryloxy, hydroxyl, amino, cyano, carboxylic acid, amide, ester, alkyl carbonyl, alkylsulfo or diallrylsulfonyl radicals, or hydrogen atoms; R; and R; can be hydrogen atoms, alkyl radicals such as methyl, ethyl, etc., or cyano radicals.

Typical examples of specific compounds having one of the above structural formulas include the following:

1-[4-(benzoxazol-2-yl phenyl] -4-phenylbuta- 1,3 -diene 4- (benzoxazol-Z-yl stilbene 4,4-di- 5,7-di-t-pentylbenzoxazol-Z-yl) stilbene 4,4'-di- (benzoxazol-Z-yl) stilbene 4,4'-di- (benzoxazol-Z-yl) -2-methyl stilbene 4,4'-di- (benzoxazol-Z-yl) -2,2'-dimethyl stilbene 4,4'-di- G-methoxybenzoxazol-Z-yl) stilbene 4,4'-di- (benzoxazol-Lyl) -2-aminostilbene 4,4-di- (benzoxazol-Z-yl) -2-hydroxystilbene 4,4'-di- (benzoxazol-Z-yl) -2-chlorostilbene 4,4'-di-(benzoxazol-2-y1)-2-cyanostilbene The above compounds may be prepared in accordance with the method described in British provisional application 47,527/62, filed Dec. 17, 1962.

Our novel fluorescent compositions are incorporated to advantage in photographic elements, paints, inks, plasticizers, etc.

When our fluorescent compositions are to be incorporated in photographic elements, it is advantageous to incorporate them i hydrophilic colloid binders including natural materials, e.g., gelatin, albumin, a'gar agar, gum arabic, alginic acid, etc. and synthetic materials, e.g., polyvinyl alcohol, polyvinyl pyrrolidone, cellulose esters, partially hydrolyzed cellulose acetate, etc. The fluorescent composition is advantageously coated in most monochromatic photographic print materials either in the light-sensitive emulsion layer or in a layer between the white coated support and the light-sensitive layer. In photographic color print material which generally comprises a white reflecting support,,for example, a barytacoated paper having separate blue-, greenand redsensitive layers over the white layer, our fluorescent compositions can be coated in the hydrophilic colloid layer containing the red-sensitized silver halide and cyandye-forming coupler as the outermost light-sensitive layer, or may be incorporated in a hydrophilic colloid layer directly under the red-sensitive incorporated cyan coupler layer with the blueand green-sensitive layers coated below. Where the color-photographic element has an ultraviolet absorbing filter layer, this is usually coated under the layer containing our fluorescent compositions.

Our fluorescent agents are used in our fluorescent compositions over a wide range of concentrations,the optimum concentration being readily determined for a given agent and photographic element by methods well known in the art. The optimum concentration depends upon a number of factors including the particular fluorescent agent, the particular photographic element, and the results desired; however, usually enough fluorescent agent is used so that when it is coated, the fluorescent agent will be coated in the range of from about 1 mg. to about mg. per square foot, preferably in the range from about 5 mg. to about 35 mg. per square foot.

Enough dispersing solvent, i.e., a diester of a mono cyclic aromatic acid and an alkyl substituted cyclohexanol is used in our fluorescent composition to dissolve the fluorescent agent. An excess of solvent may be used, if desired, however, usually only a small excess is used. The optimum amount of solvent used for a given amount of fluorescent agent will depend upon the particular fluorescent agent and solvent used and is readily determined by methods well known in the art.

As noted above, the fluorescent agents can be incorporated in color print material in the outermost layer containing coupler capable of forming a dye which coacts with the fluorescent agent to extinguish fluorescene in those areas, and only those areas, where the dye is produced by color development. The manner in which a dye functions to extinguish fluorescence is not known, and whether a dye possesses this function cannot be predicted. However, many couplers are known to produce dyes which possess this function. Particularly useful couplers which form dyes that extinguishfluorescence are the cyan-forming phenolic couplers. (As used herein, the term phenolic couplers is used broadly as inclusive of both .phenolic and naphtholic couplers.) Typical useful phenolic couplers include those described in Us. Patent 2,423,730 and the following:

Couplers producing cyan images 5- p-amylphenoxyb enzenesulfonamino -1-naphthol 5- (N-benzyl-N-naphthalenesulfonamino) -1-'naphthol 5 (N ben zyl-N-n-valeryl amino) -1-naphtho1 S caprQyIamino-l-naphthol 2-chlor o -5 N-n-valeryl-N-p-is o propylbenzyl amino) l-naphthol 2,4-dichloro-5- p-nitrob enzoyl-p-o-hydroxyethylamino ,l-naphthol' p 2,4-dichloro-5-palmitylaniino-l-naphthol 5-diphenylethersulfonamido-l-naphthol l-hydroxy-Z-(N-isoamyl-N-phenyl)-naphthamide 1-hydroxy-2-(N-p-sec. amylphenyl)-naphthamide S-hydroxy-lea-naphthoyl-1,2,3,4-tetrahydroquinoline 2-lauryl-1-chlorophenol 1-naphthol-2-carboxylic-a-naphthalide lfrnaphthol-S-sulfO-cyclohexylamide 5phenoxyacetamino-1-naphthol SAp-phenyIprQ iQnylamino-1-naphthol Monochlor-S (N-y-phenylpropyl-N-p-sec. amyl-benzoyl- "amino-l-naphthol Any suitable ultraviolet absorber may be incorporated in' the, photographic print materials of the invention to provideprotection for .dyes which deteriorate whensubjected to ultraviolet radiation. -:These agents. may be incorporated in emulsion or hydrophilic colloid spacing layers. Typical useful ultravioletfabsorbers are the thiazolidone derivatives disclosed in US. Patents 2,739,888,; 2,739,971 and 2,808,330. 7

EXAMPLE 1 v Fluorescent composition A *.14,4f5di-(5,7-di-t-pentylbenzoxazol-Lyl)stilbene (0.1 g.) was dissolved in di-(Z-methylcyclohexyl) terephthalate (13"ml;)- at 100 'C.-,'I he--solutio n. was added to 10% gelatin,( 30 ml.) (containing a.5 aqueous solution of tri-isopropylnaphthalene sulfonic acid (0.88 ml.) as a dispersing agent) at 40 C. with rapid stirring. The rapid stirring was continued for 10 minutes while raising the temperature to 65 C. A further" quantity of 10% gelatin wasadded(ZIO TniIJ'Tfand the stirring continued for10 minutes more.

Fluorescent compositionB (control outside our-invention)- r 4,4'-di-(5,7 di tpentylbenzoxazol 2-yl) stilbene (0.1-

g'.) was dissolved in=dibutyl phthalate,(13 ml.) and the solution dispersed in a 10% gelatinsolution ml.) at

' Fluorescent composition C (control outside our invention) 4,4-di-'(5;7-di-t-pentylbenzoxazol-2-yl)stilbene (0.1 g.) was dissolved in diethyl lauramide at C. and the solution dispersed in 10% gelatin: (30 ml.) at.40 C. with rapid stirring for one minute. A further solution (210. ml.) was addedzandthe stirring continued for one minute.

The fluorescent coating compositions A, B and C were each coated-.onnon-fluorescent paper (over a geIatin pad of 6 ml. of 10% gelatin per sq. ft.).. at 10 mlpdispersio'n per sq. ft. l 1.

Thearfluorescent emission and the whiteness of the coatings were measured by' the method described below. The' coatings were then exposed to north daylight for 32. hours; and the fluorescence and whiteness again measured wA-Ha'rrison Fluorescence Measuring Unitwas used for all these measurements. The sample was illuminated by light fromua fluorescent "tube and the reflected light passed via-'4'filters selected in turn to a photocell. connected toa galvanometer. The galvanometer deflections were recorded and :these values converted into numerical estimation of whiteness using vpublishediformulas.

Fluorescent measurements The light source used was an ultraviolet emitting tube. The light emanating from the sample, therefore, originated only from the fluorescent compound. As the emission was in the ultraviolet region in the spectrum, it was-adequately measured by the response through'the wide band blue filter. The results are given in Table I.

TAB LE I Response through B2 filter After Percentage 32 hours fluorescence Coating of Fluorescent Composition Untaded exposure retained The results show that fluorescent composition A supplied greater fluorescent emission initially than fluorescent compositions B and C, and after 32 hours exposure to light retains considerably more fluorescence than Coatings B and C.

, Whiteness measurements The measurements were made using fluorescent tube simulating daylight characteristics including the UV. component. Whiteness is a subjective phenomenon which is .acomplex function of the sample colored and its re, flective factor (brightness). It is not always practicable to combine these properties into a single number denoting whiteness. Many different Whiteness formulas existall have limitations. One such (Taubes formula) is regarded by (LOpt. Soc. Am. 50, (1) 1960, p. 44) as satisfactory for materials containing fluorescent agents. Theformula is W=4B-3G where W equals Whiteness, B equals blue tri-stimulus reflectance, G equals green tri-stimulus reflectance. Substituting the values obtained on the fluorescent measuring units in this fourth, the result of Table 2 were obtained.

TABLE 2 Whiteness (Taube) After Percentage 32 hours whiteness Coating of Fluorescent Compostion Unfaded exposure retained Coating composition A was repeated using in place of the di-(Z-methylcyclohexyl)terephthalate, the phthalates, isophthalates, and terephthalates of 2-methyl-, 3-methyl-, 4- methyl-, 2-ethyl-, 2,5-dimethyl-,' 3,5-dimethyl-, 3,4-dimethyl 3,3,5-trimethyl-, 2-'n-butyl-, 4-t-butyl-, and 2-i sopropyl 5 methylcyclohexanol. Also jdi- (2-methylcyclohexyl)t"erephthalate was used as the solvent for 3-phen'yl-7 [Z-(dimethyla-minoethyl) ureido]coumarin, 2,5-di (5 t butylbenzoxazol-Z-yl)thiophene, mixtures of 4,4-di-(5,7- di-t-pentylbenzoxazol-Z-yl)stilbene and 2,5-di-(5-t-butylbenzoxazol-2 yl)thiophene, and a mixture of 2,5-di-(5-t? butylbenzoxazol 2 yl)thiopliene and 3-.phenyl-7-[2-(dii methylaminoethyl)ureido]coumarin in other examples of improved stability of fluorescence and whiteness compared to the control used, that is, coating of fluorescent composition B as described in Example 1.

EXAMPLE 3 Similar dispersions are made using di-(2-methylcyclohexyl)terephthalate as a solvent and 2,5-di-(-t-butylbenzoxazol-2-yl)thiophene, and a mixture of 2,5-di-(5-tbutylbenzoxazol-2-yl)thiophene and 4,4'-di-(5,7dit-pentylbenzoxazol-Z-yl)stilbene as the fluorescent agents in color print materials. These color materials are exposed to a step wedge and developed with a developer containing 4- amino-N-ethyl-N-[B-methane sulfonamido ethyl]m-toluidene sesquisulfate monohydrate, as the active developing agent and stopped, fixed, bleached, and hardened in the usual way. The prints thus obtained shown enhanced stability to fluorescence and whiteness compared to color photographic elements in which the fluorescent brightening composition is the same excepting that di-butyl phthalate is used as a solvent.

EXAMPLE 4 Fluorescent compositions are made using the solvent and fluorescent agents of Example 3 and dispersing them in black-and-white print layers. These coatings are exposed to a step wedge after drying and developed with a conventional aqueous alkaline hydroquinone developer solution, fixed and washed inthe usual way The prints thus obtained show strong fluorescence and enhanced stability of fluorescence and whiteness compared to similar black-and-white photographic elements containing similar dispersions but in which the di-(Z-methylcyclohexyl)terephthalate is replaced with dibutyl phthalate.

EXAMPLE 5 8 m1. of 10% gelatin per sq. ft.) at 10 mll of dispersion per sq. ft. as Coatings D, E, F and G, respectively.

The fluorescent emissions of Coatings D through G were measured by the method described in Example 1. Coatings were then exposed to north daylight for 32 hours and the fluorescence again measured. The results are summarized in Table 3.

TABLE 3.RESPONSE THROUGH B2 FILTER Alter 19,000 toot candle hours 1 ex e Percentage to north fluorescence Fluorescent Coating ..Unieded daylight retained D 135 39' 29 E 138 74 .llr."-fi F 154 70 G (control) 140 22 16 The results show that in all cases there is a very sub stantial improvement in the percentage fluorescence retained in Coatings D, E and F, as compared to control Coating G, which is outside of the invention. Coating F had a substantially higher fluorescence initially as compared to the control.

Example 10 4,4'-di-(5,7-di-t-pentylbenzoxazol-2-yl)stilbene was dissolved in various solvents at a concentration of 3 mg. per liter (4x10- molar). These solutions were faded in bulk by exposure to U.V. radiation of wavelength 365 mg. The fluorescent emission was measured from time to time by means of a photocell and photomultiplier. The percent emission compared with the initial emission-is 4,4'-di-(5,7-di-t-pentylbenzoxazol 2 yl)stilbene (0.05 35 giveninTable 4.

TABLE 4 Percentage emission (time in hours) Solvent 0 1 2 3 4 5 8 Dibutyl phthalate 100 92.3 85.9 82.0 82.0 80.8

Tricresyl phosphate 100 96.2 92.4 88.6 84.8 81.0 77.2

Cyclohexane-1,4-dimethanoldilormate. 100 95.4 92.3 89.2 88.5 86.9

Cyclohexanol 100 96.6 93.4"9L3 89.3 88.0 86.0

Dl-(2-methylcyclohexyl)terephthalate 100 100 100 100 100 r 100 .100

g.) was dissolved in di-2-(methylcyclohexyl)isophthalate (6.5 ml.) and the solution dispersed in a 10% gelatin solution (15 ml.) (containing a 5% aqueous solution of tri-isopropyl naphthalene sulfonic acid sodium salt (0.2 ml.) as a dispersing agent) with rapid stirring for 5 minutes. A further quantity of 10% gelatin (105 ml.) was added and the stirring continued for 5 minutes,

EXAMPLE 6 A dispersion was prepared as in Example 5 except that di-(x-methylcyclohexyl)isophthalate (where x denotes a mixture of 2, 3 and 4-methyl substituted cyclohexyl) was used in place of di-2-methylcyclohexyl isophthalate.

EXAMPLE 7 A dispersion was made as in Example 5, except that di- (x-methylcyclohexyl)phthalate (where x denotes a mixture of 2, 3 and 4-methyl substituted cyclohexyl) was instead of di-Z-methylcyclohexyl isophthalate.

EXAMPLE 8 The results show that "there was no decrease in the fluorescent emission for the fluorescent composition having di-(Z-methyl-cyclohexyl)terephthalate as the solvent following 6 hours of exposure to U .V. radiation while the fluorescent compositions containing di-butyl phthalate, tricresyl phosphate, cyclohexane-1,4-dimethanoldiformate and cyclohexanol, respectively, as the solvent produced only 80.8%, 81.0%, 869% and 88.0%, respectively, of their initial fluorescent emission following 5 hours exposure to the ultraviolet radiation. These results demonstrate the technical advance provided by use .of our fluorescent compositions.

'Ihe fluorescent compositions of. our invention are used to advantage for incorporationin photographic elements to increase the whiteness of the highlights in either. blackand-white print material or color print material: and have utility also as fluorescing material in fluorescent paints, inks, plasticizers,-etc. Our fluorescent compositions are characterized by having strong fluorescent emission initially as well as showing significantly improved fluores cent stability upon prolonged exposure to ultraviolet light. 1 I

The invention has been described in detail with particular reference to preferred embodiments'thereofabut it will be understood that variationsand modifications can be eifected within the spirit and scope of the invention as described hereinabove and asdefined in the:appended claims.

We claim:

1. A fluorescent composition having improved stability to prolonged exposure to light, said composition comprising an intimate mixture of:

(l) a fluorescent agent which has strong absorption of radiation in the ultraviolet region of the spectrum, high fluorescent emission in the blue region of the spectrum, and which is substantially insoluble in water, and

(2) a diester derived from a dibasic monocyclic aromatic acid and an alkyl-substituted cyclohexanol as a dispersing solvent for said fluorescent agent.

2. A composition of claim 1 in which the said ester has a melting point that is low enough so that the ester can be dispersed in aqueous gelatin and coated while remaining in liquid form.

3. A composition of claim 1 in which the fluorescent agent is selected from a group consisting of a thiophene fluorescent agent, a stilbene fluorescent agent and a coumarin fluorescent agent.

4. A composition of claim 1 in which the diester has the formula:

wherein R and R each represent an alkyl group and R R R and R each represent a member selected from the class consisting of a hydrogen atom and an alkyl radical.

5. A composition of claim 1 in which the fluorescent agent is selected from the class consisting of 4,4-di-(5,7- di-t-pentylbenzoxazol-Z-yl) stilbene, 2,5-di (S-t-butylbenzoxazol-Z-yl) thiophene, and 3-phenyl-7-[2-(dimethylaminoethyl ureido] coumarin.

6. A composition of claim 1 dispersed in a film-forming hydrophilic colloid.

7. A photographic element comprising a support having a white-reflecting surface carrying at least one lightsensitive silver halide emulsion layer and at least one layer containing dispersed therein an intimate mixture of:

(1) a fluorescent agent which has a strong absorption of radiation in the ultra-violet region of the spectrum, high fluorescent emission in the blue region of the spectrum, and which is substantially insoluble in water and (2) a diester derived from a dibasic monocyclic aromatic acid and an alkyl-substituted cyclohexanol as a dispersing solvent for said fluorescent agent.

8. A photographic element of claim 7 in which the fluorescent agent is selected from the group consisting of a thiophene fluorescent agent, a stilbene fluorescent agent and a coumarin fluorescent agent and in which the said fluorescent agent is dissolved in the said diester.

9. A photographic element of claim 7 in which the diester has the formula:

wherein R and R each represent an alkyl group, and R R R and R 13 each represent a member selected from the class consisting of a hydrogen atom and an alkyl radical, and wherein the said diester is a solvent for the said fluorescent agent.

10. A photographic element of claim 7 in which the fluorescent agent is selected from the class consisting of 10 4,4'-di-(5,7-di-t-pentylbenzoxazol-Z-yl)stilbene, 2,5-di-(5- t-butylbenzoxazol-Z-yl)thiopene, and 3-phenyl-7-[2-(dimethylaminoethyl)ureido]coumarin.

11. A photographic element of claim 7 in which the fluorescent agent is 4,4'-di- (5,7-di-tpentylbenzoxazol-2- yl)stilbene and the diester is di-(2-methylcyclohexyl)- terephthalate.

12. A photographic element of claim 7 in which the fluorescent agent is 3 phenyl 7[2-dimethylaminoethy1) ureido]coumarin and the diester is di-(4-t-butylcyclohexyl phthal ate.

13. A photographic element of claim 7 in which the fluorescent agent is 2,5-di(5-t-butylbenzoxazol-2-yl)thiophene and the diester is di-(3,3,S-trimethylcyclohexyl)- phthalate.

14. A photographic element comprising a support having a white surface, a plurality of coatings over said white surface, which coatings include light-sensitive coatings, one coating being sensitive to the blue region of the spectrum, another being sensitive to the green region of the spectrum and another being sensitive to the red region of the spectrum, the red-sensitive coating being the outermost coating, said red-sensitive coating containing a dispersion of a solution of:

(1) a fluorescent agent which has a strong absorption of radiation in the ultraviolet region of the spectrum, high fluorescent emission in the blue region of the spectrum and which is substantially insoluble in water, and

(2) a diester derived from a dibasic monocyclic aromatic acid and an alkyl-substituted hexanol as a dispersing solvent for said fluorescent agent.

15. A photographic element comprising a support with a white surface and a plurality of coatings therein including one light-sensitive coating sensitive to blue light, another light-sensitive coating sensitive to green light and another light-sensitive coating sensitive to red light, the red light-sensitive coating being the outermost lightsensitive coating, the improvement for brightening white areas of a print made from said element which comprises incorporating in the said red-sensitive coating a dispersed solution of (1) a fluorescent agent which has a strong absorption of radiation in the ultraviolet region of the spectrum, high fluorescent emission in the blue region of the spectrum and which is substantially insoluble in water, and

(2) di-(2-methylcyclohexyl)terephthalate as a dispersing solvent for said fluorescent agent.

16. A photographic element comprising a support with a white surface and at least one light-sensitive silver halide emulsion layer, the improvement for brightening White areas of a print made from said element which comprises incorporating in at least one layer of the said element a dispersed solution of:

(1) a fluorescent agent which has a strong absorption of radiation in the ultraviolet region of the spectrum, high fluorescent emission in the blue region of the spectrum, and which is substantially insoluble in water, and

(2) di-(Z-methylcyclohexyl)terephthalate as a dispersing solvent for said fluorescent agent.

References Cited UNITED STATES PATENTS 3,125,536 3/1964 OBrien 117-33.5 3,185,650 5/1965 Gurnee et al. 252--301.6

NORMAN G. TORCHIN, Primary Examiner I. R. HIGHTOWER, Assistant Examiner US. Cl. X.R.

mg? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. i- 7 Dated October 28, 1969 Inventor(s) Alan G. Bright, Miroslav V. Mijovic, David G. Saunde It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

olumn 2, line hip, Formula I that portion of the formula readin 9 10 O 0. should read 0 R 8 axi Column 3, line 11, "phenyfl should read --phenyl;] Column 3, line 1L5, Formula IV that portion of the formula readi:

I 5 should read 5 R5 R Column 6, line 28, "reflective" should read --reflectance--; Column 6, line 37, "fourth" should read --Iormu1a--.

Column 9, line 65, Claim 9 that portion of the formula reading R 0 10 $0 should read R Q R 9 SIGNED AND SEALED L JUN 2 197 6 .Attest:

Edward M. Fletcher, Ir. m- J8- Anesdqg Officer Comissianer of Patent! 

